Conventional floorboards are usually joined by means of glued tongue-and-groove joints along their long sides and short sides. In laying, the boards are moved together horizontally, a projecting tongue along the joint edge of a first board being inserted into the groove along the joint edge of a second board. The same method is used for long sides as well as short sides. The tongue and groove are designed merely for such horizontal joining and with special regard to the design of glue pockets and glue surfaces to enable efficient adhesion of the tongue in the groove. The tongue-and-groove joint has cooperating upper and lower abutment surfaces which position the boards vertically to obtain a planar upper surface of the completed floor.
In addition to such conventional floorings that are joined by means of glued tongue-and-groove joints, floorboards have recently been developed which instead are mechanically joined and which do not require the use of glue.
WO 94/26999 discloses a locking system for mechanical joining of building boards, especially floorboards. The boards can be locked by means of this locking system both perpendicular to and in parallel with the principal plane of the boards on long sides as well as short sides. Methods for making such floorboards are disclosed in SE 9604484-7 and SE 9604483-9. The basic principles of designing and laying the floorboards as well as the methods for making the same that are described in the above three documents are applicable also to the present invention, and therefore the contents of these documents are incorporated by reference in the present description.
With a view to facilitating the understanding and the description of the present invention, and the understanding of the problems behind the invention, a brief description of floorboards according to WO 94/26999 follows, reference being made to FIGS. 1-3. This description of the prior-art technique will in applicable parts also be considered to apply to the following description of embodiments of the present invention.
A floorboard 1 of known design is illustrated from below and from above in FIGS. 3a and 3b, respectively. The board is rectangular with a top side 2, an underside 3, two opposite long sides 4a, 4b which form joint edges, and two opposite short sides 5a, 5b which form joint edges.
Both the long sides 4a, 4b and the short sides 5a, 5b can be joined mechanically without any glue in the direction D2 in FIG. 1c. To this end, the board 1 has a planar strip 6 which is mounted at the factory and which extends along one long side 4a, said strip extending along the entire long side 4a and being made of a flexible, resilient aluminium sheet. The strip 6 can be mechanically fixed according to the embodiment illustrated, or fixed by means of glue or in some other fashion. Other strip materials can be used, such as sheet of some other metal, and aluminium or plastic sections. Alternatively, the strip 6 can be integrally formed with the board 1, for example by some suitable working of the body of the board 1. However the strip 6 is always integrated with the board 1, i.e. it is not mounted on the board 1 in connection with laying. The width of the strip 6 can be about 30 mm and its thickness about 0.5 mm. A similar, although shorter strip 6′ is arranged also along one short side 5a of the board 1. The edge side of the strip 4 facing away from the joint edge 4a is formed with a locking element 8 extending along the entire strip 6. The locking element 8 has an active locking surface 10 facing the joint edge 4a and having a height of, for instance, 0.5 mm. In connection with laying, the locking element 8 cooperates with a locking groove 14, which is formed in the underside 3 of the opposite long side 4b of an adjacent board 1′. The short side strip 6′ is provided with a corresponding locking element 8′ and the opposite short side 5b has a corresponding locking groove 14′.
For mechanical joining of long sides as well as short sides also in the vertical direction (direction D1 in FIG. 1c), the board 1 is also formed, along one long side 4a and one short side 5a, with a laterally open recess 16. The recess 16 is defined downwards by the associated strips 6, 6′. At the opposite edges 4b and 5b there is an upper recess 18 defining a locking tongue 20 cooperating with the recess 16 (see FIG. 2a).
FIGS. 1a-1c show how two such boards 1, 1′ can be joined by downwards angling. FIGS. 2a-2c show how the boards 1, 1′ can instead be joined by snap action. The long sides 4a, 4b can be joined by both methods, whereas the short sides 5a, 5b—after laying of the first row—are normally joined after joining of the long sides, and merely by snap action. When a new board 1′ and a previously laid board 1 are to be joined along their long sides according to FIGS. 1a-1c, the long side 4b of the new board 1′ is pressed against the long side 4a of the previously laid board 1 according to FIG. 1a, so that the locking tongue 20 is inserted into the recess 16. The board 1′ is then angled downwards to the subfloor 12 according to FIG. 1b. Now the locking tongue 20 completely enters the recess 16 while at the same time the locking element 8 of the strip 6 enters the locking groove 14. During this downwards angling, the upper part of the locking element 8 can be active and accomplish a guiding of the new board 1′ towards the previously laid board 1. In the joined state according to FIG. 1c, the boards 1, 1′ are locked in both D1 direction and D2 direction, but can be displaced relative to each other in the longitudinal direction of the joint.
FIGS. 2a-2c illustrate how also the short sides 5a and 5b of the boards 1, 1′ can be mechanically joined in both D1 and D2 direction by the new board 1′ being moved essentially horizontally towards the previously laid board 1. This can be carried out after the long side 4b of the new board 1′ has been joined as described above. In the first step in FIG. 2a, beveled surfaces adjacent to the recess 16 and the locking tongue 20 cooperate so that the strip 6′ is forced downwards as a direct consequence of the joining of the short sides 5a, 5b. During the final joining, the strip 6′ snaps upwards as the locking element 8′ enters the locking groove 14′. By repeating the operations shown in FIGS. 1 and 2, the laying of the entire floor can be made without glue and along all joint edges. Thus, prior-art floorboards of the above-mentioned type are mechanically joined by, as a rule, first being angled downwards on the long side, and when the long side is locked, the short sides are snapped together by horizontal displacement along the long side. The boards 1, 1′ can be taken up again in reverse order, without damaging the joint, and be laid once more.
In order to function optimally, the boards, after being joined, should along their long sides be able to take a position where there is a possibility of a small play between the locking surface 10 and the locking groove 14. For a more detailed description of this play, reference is made to WO 94/26999.
In addition to the disclosure of the above-mentioned patent specifications, Norske Skog Flooring AS (licensee of Valinge Aluminium AB) introduced a laminate flooring with a mechanical joining system according to WO 94/26999 in January 1996 in connection with the Domotex fair in Hannover, Germany. This laminate flooring marketed under the trademark Alloc® is 7.6 mm thick, has a 0.6 mm aluminium strip 6 which is mechanically fixed on the tongue side and the active locking surface 10 of the locking element 8 has an inclination of about 80° to the plane of the board. The vertical joint is formed as a modified tongue-and-groove joint, where the term “modified” relates to the possibility of joining groove and tongue by inwards angling.
WO 97/47834 (Unilin) discloses a mechanical joining system which is essentially based on the above prior-art principles. In the corresponding product which this applicant has begun to market in the latter part of 1997, biasing between the boards is strived for. This leads to high friction and difficulties in angling together and displacing the boards. The document shows a plurality of embodiments of the locking system.
Other prior-art locking systems for mechanical joining of board material are disclosed in GB 2,256,023, which shows one-sided mechanical joining for the provision of an expansion joint, and in U.S. Pat. No. 4,426,820, which shows a mechanical locking system which, however, does not allow displacement and locking of short sides by snap action.